1. Field of the Invention
The invention relates to a method of dry etching of semiconductor wafers and, more particularly, to a method of etching silicon using gas mixtures comprising fluorine (F) and oxygen (O).
2. Description of the Background Art
Trenches formed in semiconductor substrates have many uses in producing integrated circuits including isolation, capacitor formation, transistor formation, and the like. One important use of trenches is in the formation of gate structures for field effect transistors. In a conventional gate structure, trench walls are formed between a source region and a drain region. The walls and bottom of the trench are coated with a thin dielectric material, which is then conformally coated with polysilicon such that the polysilicon forms a gate electrode for a transistor.
Traditionally, gate trenches are formed using an anisotropic chemical or reactive ion etching of a masked silicon substrate. Etching chemistries utilize combinations of such chemicals as hydrogen bromide (HBr), chlorine (Cl.sub.2), oxygen (O.sub.2), nitrogen fluoride (NF.sub.3), sulfur hexafluoride(SF.sub.6), and nitrogen (N.sub.2). For example, an HBr/Cl.sub.2) chemistry can provide a silicon etch rate of about 5000 .ANG./min. with a photoresist selectivity (defined as the ratio of the etch rate of silicon to that of photoresist) of between 3:1 to 4:1. To improve the throughput for wafer processing, it is desirable to maximize the silicon etch rate, especially for applications such as trench etching. In general, however, an increase in the silicon etch rate also decreases the photoresist etch selectivity.
Therefore, a need exists in the art for a silicon etching process having an increased silicon etch rate and an enhanced mask selectivity.